Apparatus for the radiation or reception of electromagnetic waves



Jan. 18, 1949. c, CORK T 2,459,768

APPARATUS FOR THE RADIATION OB RECEPTION 0F ELECTROMAGNETIC WAVES 'FiledMay 19. 1944 Patented Jan. 18, 1949 APPARATUS FOR THE RADIATION R RE-CEPTION OF ELECTROMAGNETIC WAVES Edward Cecil Cork and MichaelBowman-Manifold, Ealing, London, England, assignors to Electric &Musical Industries Limited, Hayes, England, a company of Great BritainApplication May 19, 1944; Serial No. 536,324 In Great Britain May 21,1943 6 Claims.

1 This inventionrelates to apparatus for the radiation or reception ofelectromagnetic waves. It is sometimes a requirement to provide aradiating or receiving element of electromagnetic waves which possessesat least in one plane a directivity pattern like that of a dipoleelement but not at the same time possessing the marked frequencyselectivity of such an element. A

simple way of obtaining a radiating or receiving element that ismarkedly unselective is to employ for the purpose a portion ofelectromagnetic guide open at one end, at which end electromagneticwaves may be radiated or received. Such devices are known commonly aselectromagnetic horns or wave-guide aerials. However, as commonlyemployed, radiating or receiving elements of this kind are bulky ascompared with a dipole element and have directivity patterns sharperthan that of a dipole. It is an object of the present invention toprovide a radiating or receiving element of electromagnetic guidecharacter in which these difiiculties are overcome.

Thus, according to a feature of the invention, there is providedtransmitting or receiving apparatus for the radiation or reception ofelectromagnetic waves or" a given wavelength comprising a radiating orreceiving element in the form of a tubular conductor having dimensionsin a plane lying transversely of said conductor which in one directionare small compared with those in a direction perpendicular thereto, theratio ofsaid dimensions being at least twelve to one with the smallerdimensions no larger than one-sixth of the wavelength of the transmittedor received I waves. The apparatus operates to radiate or receiveelectromagnetic waves polarised so that the electric component of forcelies in the direction of said small dimensions. Waves of the H10 modeare. then set up in the space enclosed by said tubular conductor. Thedirectivity pattern of the apparatus in a plane parallel with theelectric component force is a single lobe substantially as is obtainedwith a dipole, but is more concentrated in a plane normal to theelectric component of force depending upon the magnitude of the largerdimensions of cross-section of said tubular conductor. By choosing thesedimensions sufliciently large a very high degree of directivity may beobtained in the latter plane. On the other hand, if said dimensions arechosen to be substantially one-half wavelength at the operatingfrequency then the directivity in said latter plane is not appreciablydifferent from the broad lobe of a dipole. As will be explained morefully later it is possible to provide an aerial according to theinvention pact character. 7 Radiating elements as just described aresuitable when arranged in an array for providing-a directivity patternin a given plane which is substantially uniform in all directions. I I

Thus, according to another feature of the invention there is providedapparatus for the radiation of electromagnetic waves comprising aplurality of radiating elements each in the form of a tubular conductorhaving dimensions in a plane lying transversely of said conductor whichin one direction are small compared with those in a directionperpendicular thereto, said radiating elements being radially arrangedso that said waves Will be radiated by said apparatus substantiallyuniformly inall directions in a plane. Such apparatus may be arranged toradiate waves having the electric component of force lying parallel tosaid plane or, normal thereto. Since wave-guide radiators are highlyunselective such apparatus is particularly suitable for radiating Wavesof a wide range of frequencies as in television transmission. s

In the use of electromagnetic horns or waveguide aerials it is foundthat. the directivity diof highly comagrams may be distorted or may tendto be un- V stable. For example, in apparatus where a single hollowconducting element is employed there may occur in the directivitydiagram beside the single forwardly-directed lobe other lobes which aredirected backwardly. Such other lobes may be undesirable. Thesedifficulties arise by reason of the setting up of currents of operatingfrequency on the rim or exterior surface of the hollow conductingelement. It is a further object of the invention to overcome orreducethis difiicul'ty.

According therefore to a further feature of the invention there isprovided a wave-guide trans: mitting or receiving aerial comprising atubular conductonwherein in order to attenuate currents of a certainfrequency at the rim of said con ductor a further conductor is providedelectrical,-

ly connected to said tubular conductor and sub stantially surroundingthe latter in such a man.- ner as to present a high impedance tov saidcur.- rents at said rim.

In order that the invention may be clearly understood and readilycarried into effect, embodiments of the invention will now be describedby, way of example with reference to the accompanying drawings, in whichEli-sure l shows. the invention in. simpleform.

with the radiating or receiving element in association with a coaxialline feeder, and

Figures 2 and 3 illustrate forms consisting of four elements andsuitable for giving a circular diagram such as is required inbroadcasting.

Referring to Figure l, the radiating or receiving element is indicatedby the reference numeral l and consists essentially of a tubularconductor of rectangular cross-section free to radiate or receiveelectromagnetic waves at its open end II, but electricallyshort-circuited at its other end l2. It will be seen from the figurethat the element [0 has dimensions in cross-section with which in onedirection are small compared with those in a direction perpendicularthereto. The greater of the two dimensions of cross-section is shownvertically in Figure 1 and the ratio of the larger to the smallerdimension of said crosssection is twelve to one or greater. The greaterdimension is a half wavelength or more at the operating frequency,whilst the smaller dimension is shown horizontally and is not greaterthan one-sixth of a wavelength and is preferably of the order of aneighth of a wavelength or less. Energy is fed to or removed from theelement ID by means of the coaxial feeder line I 3 which enters at oneof the larger sides of the element ID at the point l4, and the innerconductor I 5 is continued into the space within the element in, asshown at l6, so as to be capable of exciting waves of the H mode in thespace. Preferably, the exposed continuation I6 is tuned to resonance atthe operating frequency by means of a short length of coaxial line in amanner that will be explained more fully with reference to Figure 2.Since the radiation resistance of the continuation l6 depends not onlyupon the dimensions of crosssection of the element 1 0, but also on thedistance of the element 16 from the reflecting end surface at the closedend i2 of the element [0 and from the sides of lesser dimensions, propermatching of the feeder l3 to the element I0 may be achieved by suitablelocation of the point of entry of the feeder into the side of theelement I I). Said point of entry may be located at a distance ofapproximately one-quarter of a guide wavelength from the reflecting endof the element ID to provide suitable matching of said feeder to saidelement. The portion of the tubular conductor [0 lying in front of thefeeder may be of any length or may be omitted. For the purpose ofreducing the physical dimensions of the arrangement or for preventingthe entry of moisture of other deleterious matter into the aerial, thespace within the element I 0 may be filled With a dielectric materialsuch as the material known by the registered trade-mark Polythene. Thearrangement may thereby be rendered highly compact.

In order to reduce the tendency for the aerial toset up currents at theoperating frequency on the rim or exterior surface of the conductor 10,a further conductor" is provided surrounding the conductor l0 andelectrically connected thereto. The effective length of said conductorII, he, its length from the open end of the conductor l0 towards itsrear is a quarter of a wavelength at the operating frequency so astopresent a high impedance to currents at the operating frequency.

The directional diagram of the aerial is a single lobe pointing in thedirection of the open end II of the element [0. In the plane of theelectric vector, which is the plane of the lesser dimension ofcross-section of the element 10 the lobe is broad and gradually reducesto a minimum in the direction of the closed end of the element. In theplane of the magnetic vector which is vertical with the particulardisposition of the figure there is a much greater directivity whichdepends on the greater dimension of cross-section of the element ID. Thenature of this directivity is indicated by the following table in whichvalues of the greater dimension are given in the left-hand column and inthe right-hand column the corresponding values of gain as compared witha dipole:

/2 \1.1 A3.0 fil\4.4-. 276.8

These values can be obtained with the smaller dimension of cross-sectionequal to an eighth of a wavelength and when rim currents at the open endof the element I0 are attenuated by the conductor II.

In Figure 2 there is shown a radially-disposed arrangement of elements20 similar to the element l0 described with reference to Figure l andjoined to form a cruciform structure. The elements 20 have their greaterdimension of cross-section lying in the plane of the cruciform. Thisdimension is of the order of the operating wavelength so as to givedirective diagrams to the individual elements 20 that add up to providea substantially uniform diagram in said plane. Arranged so that thecruciform lies horizontally, as shown in the figure, the aerial is thussuitable for broadcast transmission with a vertical polarisation. Rimcurrents at the open ends of the elements 20 may be attenuated byquarter wavelength conductors (not shown but similar to that indicatedin Figure 1 by the reference numeral I 1). Waves of H10 mode are excitedin the elements 20 by means of an energising element 22 similar to thatdesignated at I6 in Figure 1 and arranged normal to the plane of thecruciform at the centre thereof. The element 22 is a continuation of thecoaxial feeding line 2|. In order to tune the energising element 22 toresonance at the operating frequency as is desirable, there is provideda further portion 23 of coaxial line the outer conductor of which isconnected to the contacting surface of the cruciform and the innerconductor of which is an extension of the energising element 22.

In order to provide a radiator of horizontal polarisation suitable forbroadcast transmission, a cruciform structure may be formed of fourradially-arranged radiating elements 24 having their greater dimensionof cross-section lying vertically instead of horizontally, as in Figure2. Such an arrangement is illustrated in Figure 3. Each radiatingelement is provided with an energising element 25 and these elementsconsist of the bent end portions of a feeding structure comprising fourradial arms connected to the inner conductor of the coaxial line 21. Thefeeding structure is arranged to lie in the mid-plane of the cruciform.The feeding structure is tuned to resonance at the operating frequencyby the provision of the further portion of coaxial line 23 after themanner of the like arrangement of Figure 2. As with the arrangement ofFigure 2, quarter-Wave conductors I! may be provided at the open ends ofthe radiating elements (these not however being shown in the figure) Inany of the above arrangements the radiating elements may be flared outtowards their openings and they may also be fed by guide type feedersinstead of coaxial lines as described.

What we claim is:

1. Apparatus for the radiation of electromagnetic waves comprising aplurality of radiating elements each in the form of a tubular conductorhaving dimensions in a plane lying transversely of said conductor whichin one direction are small compared with those in a directionperpendicular thereto, said radiating elements being radially arrangedso that said waves will be radiated by said apparatus substantiallyuniformly in all directions in a plane and each of said radiatingelements being energized by an energizing element including a portion ofthe inner conductor of a coaxial line disposed substantially at thecenter of the radially-arranged radiating elements, the outer conductorof said coaxial line being connected to said tubular conductors.

2. Apparatus for the radiation of electromagnetic waves comprising apluralit of radiating elements each in the form of a tubular conductorhaving dimensions in a plane lying transversely of said conductor whichin one direction are small compared with those in a directionperpendicular thereto, said radiating elements being radially arrangedso that said waves will be radiated by said apparatus substantiallyuniformly in all directions in a plane, said elements being so arrangedthat said small dimensions lie normally to said plane of radiation, saidradiating elements being energized by a single energizing elementcomprising an integral portion of the inner conductor of a coaxial linedisposed substantially at the center of said radially-arranged radiatingelements, the outer conductor of said coaxial line being connected tosaid tubular conductors.

3. Apparatus for the radiation of electromagnetic waves comprising aplurality of radiating elements each in the form of a tubular conductorhaving dimensions in a plane lying transversely of said conductor whichin one direction are small compared with those in a directionperpendicular thereto, said radiating elements being radially arrangedso that said Waves will be radiated by said apparatus substantiallyuniformly in all directions in a plane, said elements being so arrangedthat said small dimensions lie in said plane of radiation, saidradiating elements being energized respectively by energizing elementscarried by radially disposed conductors emanating substantially from thecenter of the radially-arranged radiating elements.

4. Apparatus for the radiation of electromagnetic waves comprising aplurality of radiating elements each in the form of a tubular conductorhaving dimensions in a plane lying transversely of said conductor whichin one direction are small compared with those in a directionperpendicular thereto, said radiating elements being radially arrangedso that said waves Will be radiated by said apparatus substantiallyuniformly in all directions in a plane, said elements being so arrangedapparatus substantially uniformly in all directions in a. plane, saidelements being so arranged that said small dimensions lie in said planeof radiation, said radiating elements being energized repectively byenergizing elements carried by radially disposed arms connected to theinner conductor of a coaxial line, the outer conductor of said coaxialline being connected to said tubular conductors.

6. Apparatus according to claim 1 wherein the ratio of said dimensionsis at least 12 to 1 with the smaller dimensions being'no larger thanoneeighth of the wavelength of a source of waves connected to saidapparatus.

EDWARD CECIL CORK.

MICHAEL BOWMAN -MANIFOLD.

REFERENCES CITED The following references are of record in the file ofthis patent:

